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Measuring habitat quality in the Boston Harbor Islands using the biogeography of ant diversity

Adam Clark - Harvard College

Initial Report:

In 2002, members of the Boston Harbor Island Partnership worked together to plan future development and preservation on the Boston Harbor Islands. As a part of this effort, the islands were divided into management groups, stressing preservation of unique features such as natural beauty, historical significance, or ease of visitor access.

It would be helpful in this effort to have a way to compare habitats within the Boston Harbor Islands and assess their health and diversity. The All Taxa Biodiversity Inventory, an effort to collect and record the organisms living on each of the Boston Harbor Islands, offers a great opportunity to do this. Since species diversity – a measure of the number of species, and individuals per species, present in a given region – is strongly affected by habitat type and quality, change in diversity between islands can be a good measure of differences between the habitats themselves.

Over the past summer, I collected data on ant diversity on six islands: Spectacle, Calf, Snake, Thompson, Grape, and Langlee. I used these data to approximate a species-area curve for ants on the Boston Harbor Islands. This model allowed me to estimate the number of ants that an island was “expected” to have based solely on its size.

Langlee varied the most form this expected value, with about a third more species than predicted. While a number of factors could have contributed to this, such as distance from the mainland, types of available access, or the number of yearly visitors, the most convincing argument came from habitat type. Simply put, the wooded terrain on Langlee provided habitat for more species of ants than did the habitats on some of the other islands.

I am continuing to identify ants and analyze data from more islands this year. Adding data from other biodiversity research projects on the Boston Harbor Islands, such as Stephanie Madden’s work on carabid beetles, should help greatly in refining results. Ultimately, I would like to be able to provide feedback for island managers, by comparing and qualifying habitats across the islands based not only on the ants found in those habitats, but on island ecosystems as a whole.

January 2010 Update:

Ants have been sampled as part of the ATBI every summer since 2005, and about 50 species have been recorded. In 2009, I used litter samples on Calf, Great Brewster, Langlee, Ragged, Spectacle, and Thompson Islands to search specifically for ants, collecting 27 species. Detailed habitat maps were also made for each island. Sites were searched at the beginning and end of the summer to examine both the phenology and response to disturbance of ant communities on the islands. I identified five "communities" - that is, groups of ant species that co-occur more often than expected by chance - and used these communities, the habitat maps, and remote sensing data from Landsat imaging to project the likely changes in ant community structure over the next few years.

As of this year, all ant specimens have been pinned, identified to species, and entered into the project's database. Future projects for the coming semester will include comparing the distribution of invasive species of ants to insects in other families, and assessing the effectiveness of using ants as an indicator species for other taxa. I'd also like to use remote sensing to build accurate habitat maps of all ten islands that have been sampled intensively as part of the ATBI, and examine how community structure changes depending on habitat type contiguity.